Fetomaternal hemorrhage can result from different types of trauma and may be followed by fetal anemia, fetal death, or isoimmunization. We prospectively studied the frequency and volume of fetomaternal hemorrhage, fetal well-being, abruptio placentae, and fetal outcome in 32 pregnant patients suffering recent trauma. Fetomaternal hemorrhage occurred in nine of 32 trauma patients (28%) with a mean volume of 16 ml +/- 14.3(SD). There was a statistically significant difference in the frequency and mean volume of fetomaternal hemorrhage in this group over that in gestational-age-matched controls. Neither the nature of the trauma nor the gestational age was related to the frequency or volume of fetomaternal hemorrhage. The outcome in three of the nine trauma patients who sustained fetomaternal hemorrhage was poor; fetal anemia, paroxysmal atrial tachycardia, and fetal death occurred in each one. Maternal trauma remains a significant cause of maternal and fetal morbidity and death, and the use of the Kleihauer-Betke analysis is indicated to identify fetomaternal hemorrhage. Rh-immune globulin therapy should be given to Rh-negative patients with fetomaternal hemorrhage.